Loudspeakers change an electrical signal into sound. Prior Art FIG. 1 shows a cross-sectional view of the main components of a moving-coil type loudspeaker 100. A rigid metal frame 101 attaches to a magnet 102, which subjects the air gap 108 between the magnet and the frame to a strong magnetic field. A lightweight diaphragm 103 attaches to the frame 101 and to the cylindrical shaped bobbin 107. A voice coil 104 is wound around the bobbin 107. The voice coil attaches through two voice coil wires 105 to two contacts 106. When a current is run through voice coil 104, the magnetic field in air gap 108 will interact with the current in coil 104 to create a force that causes the bobbin to move up or down depending on the direction of the electrical current. This in turn moves the diaphragm, which produces air pressure waves that result in sound.
Loudspeakers are electromechanical devices subject to failures. Some failure conditions may result in no sound at all being produced. In certain applications, it is critical that a sound is produced, even if distorted, such as is the case in medical devices, such as patient monitors. For this and other applications, a loudspeaker should have low failure rate of sound production.
Failure mechanisms of loudspeakers include voice coil wire breakage, damage of the diaphragm, diaphragm separating from the frame, and other mechanical failures. Although many of these failure mechanisms result in distorted sound, damage to the voice coil leads to no sound at all, which is undesirable in alarm sound applications.
Voice coil breakage results from mechanical stress. The voice coil moves with the diaphragm, but the wires of the voice coil attach to stationary contacts typically mounted on the loudspeaker frame. Hence the wires move and change shape with every diaphragm movement, or with every sound made by the loudspeaker.
Numerous technologies may reduce the chance of voice coil wire breakage. For example, the wires may be given extra length for strain-relief; they may be pre-shaped to allow movement, etc. The loudspeaker may also be designed such that the wires move in free space, away from other surfaces that may cause friction damage.
Despite such technologies, the voice coil wires have some probability of breaking, because they are subject to constant mechanical deformation and stress. If they break, the resulting total absence of sound is problematic in alarm applications. There is, therefore, a need for addressing these and other issues associated with the prior art.